The conventional process for the preparation of a metallic superconductor wire rod or magnet is roughly divided into two types. In the case of an alloy type material, a superconductive magnet is prepared by forming the alloy type material into an ultrafine multi-core wire mainly by utilizing a plastic deformation of the metal and winding the wire into a coil. A typical example in practical use at present is an Nb--Ti alloy. In contrast, in the case of an intermetallic compound, which has a poor workability compared with the alloy type material, a process is adopted in which the starting metal is worked to some extent to form a wire rod, the wire rod is wound into a coil, the coil is subjected to a post heat treatment to obtain a superconductive phase, and a magnet is formed (the surface diffusion process, the bronze process, and the in-situ process). Attempts to apply the technique of forming wire rods of these metallic materials to oxide superconductors have been proposed (Jpn. J. Appl. Phys., Vol. 26, No. 5, 1987, pp. L865-L866), but these attempts have no substantial practical utility because the superconductive phase in the interior of the wire is composed of a polycrystal and the crystal directions are not dispersed and are not uniform.
For a practical utilization of the oxide superconductor material, a material having a high critical current density, which is prepared by the melting method, must be formed into a long wire rod or a bulk material having a large area, but since this material has a single crystal texture, it is very difficult to obtain a superconductive phase by the conventional method adopted for metal materials, which comprises wire drawing or rolling and post heat treatment. To obtain a magnetic material from such a material, a plastic working of which is difficult, it is important to increase the length or area of an oxide superconductor having a high Jc value at a high magnetic field. In view of this problem, a primary object of the present invention is to provide an oxide superconductor of the RE--Ba--Cu--O type and a process for the preparation thereof.